Currently, for a manual vehicle, the starting process on a hill generally comprises the following four steps: (1) pressing down a brake pedal by a driver to generate a brake force, so as to assure that the vehicle is stationary on the slope; (2) then slowly releasing a clutch pedal to vibrate the vehicle body, so that the clutch enters into a partial linkage state, and thus a certain driving power is transmitted to driving wheels; (3) releasing the brake pedal and turning to press down the gas pedal, at this time the initial brake force for assuring the vehicle stationary disappears; (4) at the same time or a little later, releasing the clutch pedal by the driver, so that the clutch is or will be in a complete linkage state. Thus, enough driving power is transmitted to the driving wheels of the vehicle. The hill start of the vehicle is completed.
During the hill starting process of the manual vehicle, it is the most difficult for the driver to control the degree of step (2) among all of the four steps. In step (2), if the driver releases the clutch pedal too quickly, the clutch will enter into the complete linkage state quickly, so that the motor of the vehicle is easy to flameout. However, in step (2), if the driver releases the clutch pedal too shallowly, then sufficient driving power cannot be transmitted to the driving wheels. If so, under the circumstance that the brake force disappears in subsequent step (3), the vehicle easily rolls back along the slope, and thus may cause a danger on the road.
In order to solve this problem, the prior art provides a vehicle with a hill start assist function. However, this function must be achieved by the Electronic Stability Control (ESC). In particular, this function may be achieved by the following process: in Step (1), ESC detects the degree of the slope by an axial acceleration sensor; if the driver releases the clutch pedal too slowly, then in step (3) when the driver starts to release the brake pedal, the ESC closes the internal electromagnetic valve, the brake force remains in the braking line, and since the brake force still remains, the vehicle continues to be stationary on the slope, and would not roll back; then in step (4), the ESC communicates with the engine management system, and once the ESC detects that the drive power is enough to overcome the hill gravity during the time that the accelerator pedal is pressed down, the brake force in the braking line is released immediately. At this time, the vehicle will overcome the hill gravity owing to the driving power, though the brake force has disappeared, and thus the vehicle starts to move. As the driver continues to press down on the gas pedal, the driving power will increase gradually, so that the vehicle will run forwardly, and meanwhile the above hill start assist function will quit.
In the prior art, the above hill start assist method achieved by ESC is commonly used. This disadvantage is that the vehicle has to incorporate the ESC product. However, ESC has a low assembly percentage in the current market. For example, only 15% of cars include an ESC in the market of China. Moreover, most of the vehicles assembled with an ESC function are high-class, automatic transmission equipped cars. The percentage of vehicles having an ESC with a hill start assist function is much lower for manual transmission equipped vehicles. In addition, an ESC product is expensive, for example, the sales price is RMB 800-1000 in China.
It is also noted that, in order to maintain brake force in the braking line when the driver releases the braking pedal, the above conventional hill start assist system needs to be assembled with a particular valve: a so-called “isolation valve”. However, this type of isolation valve is usually mounted within ESC products, but is not provided within an anti-lock braking system (ABS), which is widely assembled on the vehicle.